Porous inorganic solids have found great utility as catalysts and separations media for industrial applications. The openness of their microstructure allows molecules access to the relatively large surface areas of these materials that enhance their catalytic and sorptive activities. The porous materials in use today can be sorted into three broad categories using the details of their microstructure as a basis for classification. These categories are the amorphous and paracrystalline materials, the crystalline molecular sieves and modified layered materials. The detailed differences in the microstructures of these materials manifest themselves as important differences in the catalytic and sorptive behavior of the materials, as well as in differences in various observable properties used to characterize them, such as their surface areas, the sizes of pores and the variability in those sizes, the presence or absence of X-ray diffraction (XRD) patterns and the details in such patterns, and the appearance of the materials when their microstructure is studied by transmission electron microscopy and electron diffraction methods.
The M41S family mesoporous molecular sieve is described in J. Amer. Chem. Soc., 1992, 114, 10834. Members of the M41S family mesoporous molecular sieve include MCM-41, MCM-48 and MCM-50. A member of this class is MCM-41 whose preparation is described in U.S. Pat. No. 5,098,684. MCM-41 is characterized by having a hexagonal structure with a uni-dimensional arrangement of pores having a cell diameter greater than about 13 Angstroms. The physical structure of MCM-41 is like a bundle of straws wherein the opening of the straws (the cell diameters of the pores) ranges from about 13 to 200 Angstroms. MCM-48 has a cubic symmetry and is described for example in U.S. Pat. No. 5,198,203. MCM-50 has a layered or lamellar structure and is described in U.S. Pat. No. 5,246,689.
The M41S family mesoporous molecular sieves are often prepared from aqueous reaction mixtures (synthesis mixtures) comprising sources of appropriate oxides. Organic agents, such as surfactant(s), may also be included in the synthesis mixture for the purpose of influencing the production of the M41S family mesoporous molecular sieves having the desired structure and channel size. After the components of the synthesis mixture are properly mixed with one another, the synthesis mixture is subjected to appropriate crystallization conditions in an autoclave. Such conditions usually involve heating of the synthesis mixture to an elevated temperature possibly with stirring. Room temperature aging of the synthesis mixture is also desirable in some instances.
After the crystallization of the synthesis mixture is complete, the crystalline product may be recovered from the remainder of the synthesis mixture, especially the liquid contents thereof. Such recovery may involve filtering the crystals and washing these crystals with fluids, such as, water. However, in order to remove the entire undesired residue of the synthesis mixture from the crystals, it is often necessary to subject the crystals to a high temperature calcination e.g., at 540° C., possibly in the presence of oxygen. Such a calcination treatment not only removes water from the crystals, but this treatment also serves to decompose and/or oxidize the residue of the organic directing agent which may be occluded in the pores of the crystals, possibly occupying ion exchange sites therein.
The M41S family mesoporous molecular sieve may be characterized by its structure, including extremely large pore windows, and high sorption capacity. The M41S family mesoporous molecular sieve found many applications, such as catalytic cracking, adsorption, separation, oxidation, polymerization, and pharmaceutics. However, the process of synthesizing the M41S family mesoporous molecular sieve needs expensive surfactant. In particular, costs for disposal surfactant-containing wastewater generated in the crystallization, filtration, and washing is high. It is therefore a need to improve the method of synthesizing the M41S family mesoporous molecular sieve by lowering the production cost, such as minimizing the wastewater by eliminating the filtration/washing step.
U.S. Pat. application No. 60/899,785 relates to a method for synthesizing a mesoporous molecular sieve composition, which is characterized by that at least a portion of the solvent or solvent mixture in the reaction mixture comprises wastewater from processing of the mesoporous molecular sieve made in previous synthesis batch(es), e.g., the mother liquor(s), the washing liquid(s), the cleaning liquid(s), and any combination thereof
We found a novel method of making M41S materials using synthesis mixture having high solids-content. This novel method has the advantage of making high quality M41S materials and reducing at least 50%, or even 100% of wastewater containing surfactant(s), such as, mother liquor, formed in the synthesis. Another advantage of this novel method is that it minimizes or eliminates the filtration and/or washing step(s) of the synthesis. The amount of the wastewater containing surfactant(s) generated by this novel method is reduced by at least 50% to as much as 100% as comparing with conventional method of making M41S materials. The as-synthesized M41S product of this novel method displayed similar structure and surface area as compared with the M41S product obtained with filtration and/or washing step(s). By reducing and/or eliminating at least a portion of the wastewater generated in the synthesis, the new method reduces cost of synthesizing of M41S materials and provides an environmental friendly synthesizing process.